This invention relates to an extendible rod of a type which includes at least two rod-shaped elements slidable telescopically inside each other, and an expander device acting between said elements to extend said rod and lock said rod-shaped elements in the extended position, said expander device comprising:
a first constraint member attached to one of said rod-shaped elements;
a second constraint member slidable over the other of said rod-shaped elements;
stop means for stopping the sliding movement of said second constraint member on the corresponding rod-shaped element;
a linkage performing, between said constraint members, a first stroke to actuate said stop means and a second stroke to move said constraint members away from each other; and
means of locking said linkage in a working position corresponding to a position of maximum separation of said constraint members from each other.
These rods are used as elements of modular assembly structures, or may be used for stands or supporting arrangements, especially in the photographic and movie fields, or for generic furnishings applications.
The rod is utilized by forcing its structure into a state of compression between two parallel walls through an expander device which acts between the rod-shaped elements in a direction tending to slide them off each other.
Currently known rods of this kind, while serving their intended function, have some drawbacks which complicate the operations for their installation, position setting, possible moving, and holding power against relatively compliant walls.
The last-mentioned drawback results from that a given rod should be adapted for installation between walls having different compliance characteristics. For instance, such a rod may be required to retain a firm position between reinforced concrete walls as well as between curtain walls of an exhibition booth, known for being more compliant than the former walls. The locking power in question is at all events dependent on the outward stroke of the expander device, which is to fill the conflicting demands for avoidance, with highly rigid walls, of an excessive compression on the rod-shaped elements and concurrent achievement of a secure locking where compliant walls are involved. Notice that an excessively long stroke of the expander device against highly rigid walls, in addition to involving a relevant physical effort to the installer, may harm the rod integrity.
Another limitation to known rods comes from that the linkage locking arrangement, made necessary by safety considerations and intended to prevent the rod-shaped elements from incidentally becoming loose on each other and the rod collapsing, usually requires that both hands be used for its actuation or release. This may occasionally make for difficult positioning of the rod when the latter is to be installed in hard-to-reach areas. The above two drawbacks are, of course, of greater consequence when they add together, such as where a rod with a relatively long stroke is to be fitted in an uncomfortable position between walls of low compliance.